Fluid bed furnace

ABSTRACT

A fluid bed furnace has an electric heating coil mounted on the outer face of a guard element frame which is positioned within the shell of the furnace so as to be immersed in the granular material comprising the fluid bed material. The guard element frame and heating coil comprise an assembly which can be removed as a unit from the furnace. A seal is provided on the outer face of the bottom edge of the shell to prevent entry of granular material into the layer of insulation on the outside of the shell.

United States Patent [1 1 Seelandt et al.

[ 1 July 31, 1973 I FLUID BED FURNACE [75 I lnventors: Karl H. Seelandt,C on toocook,

Y N.H.; Hobart L. Wentworth,

Barrington, Ill.

[73! Assignee: Sola Basic Industries, 'iiiEl',"T\ ii"lii?ii kee,Wis.

22 Filed: Nov. 26, 1971 {21] Appl. No.: 202,269

[52] US. Cl 13/20, 219/359, 219/369,

219/381, 219/407 [51] Int. Cl F27b 15/00, H05b 3/60 [58] Field of Search219/359, 360, 365,

[56] References Cited UNITED STATES PATENTS McAllister et al. 13/203,025,385 3/1962 Tanaka 13/20 X Primary Examiner-Roy N. Envall, Jr.Attorney-D. Vemer Smythe et al.

[57] ABSTRACT A fluid bed furnace has an electric heating coil mountedon the outer face of a guard element frame which is positioned withinthe shell of the furnace so as to be immersed in the granular materialcomprising the fluid bed material. The guard element frame and heatingcoil comprise an assembly which can be removed as a unit from thefurnace. A seal is provided on the outer face of the bottom edge of theshell to prevent entry of granular material into the layer of insulationon the outside of the shell.

11 Claims, 4 Drawing Figures PATENTEB U 3. 749.805

SHEET 1 OF 2 FIG.]

ATTORNEY PATENI JUm I975- SHEU 2 [IF 2 BY M I M. 5% ATTORNEYS FLUID BEDFURNACE This invention relates to fluid bed industrial furnaces, or onewherein air or gas is blown up through a bed of heated material.

A fluid bed industrial furnace has a bed of granular material throughwhich a fluid is directed upwardly therethrough in order to fluidize thebed. A suitable heating element, which can be electrical in nature, ismounted within the fluid bed to heat the bed. The material which is tobe subjected to the action of the fur- Such fluid bed furnaces havegenerally been electrically heated and the heating elements have notbeen positioned directly in the fluid bed in order to take advantage ofthe high heat transfer characteristics of the ordinary bed. Thefluidized medium was contained in a vessel having metallic sides outsideof whichthe heating elements were located. Prior fluid bed furnaces havehad difficulties in the maintenance thereof. When it is desired toinspect or repair the heating elements, it was first necessary to removeall of the granular material of the bed from the furnace as well as thecontaining metallic member so as to expose the heating elements. Thisnot only required considerable time on the part of skilled personnel,but invariably resulted in difficulties in removing the granularmaterial and shell and then subsequently in replacing the material andshell. Further, handling of the material caused the granular material toseep between the bottom edge of the shell and the porous diffusionbottom so that the granular material entered into the insulationmaterial positioned on the outer face of the shell. This also added tomaintenance problems since it was necessary to replace the insulationbecause the penetration of the insulation by the granular materialsignificantly decreased its insulating properties. Also, in normaloperation, the fine bed material would find its way into the insulation.

One of the objects of the present invention is to provide an improvedfluid bed furnace construction.

Another of the objects of the present invention is to provide a fluidbed furnace from which the heating element can be disassembled therefromwithout removing the fluid bed or its container.

Another of the objects of the invention is to provide an effective sealbetween the insulation on the outer face of the shell and the granularmaterial on the inside of the shell.

According to one aspect of the present invention, a fluid bed industrialfurnace may comprise an insulated shell having a porous diffusion bottommember. A bed of granular material is contained within the shell uponthe diffusion member. Means are provided for flowing a fluid upwardlythrough the bed of granularmaterial to fluidize the material. Elementguard means are removably mounted within the shell and immersed in thebed of granular material, with the guard means beingv spaced inwardlyfrom said shell. Heating element means are mounted on the outer face ofthe element guard means and spaced inwardly of the shell so that theentire assembly of the element guard means and the heating element meanscan be removed from the fluidized bed of the furnace as a unit.

The shell is provided with a blanket of insulation on its outer face.Sealing means are secured at the bottom of the shell for sealing againstthe entry of granular material under the bottom edge of the shell intothe insulation means.

The shell may be a cylinder or may have a rectangular cross section withthe guard element means having a shape similar to that of the shell butslightly smaller so as to fit therein. I

Other objects, advantages and features of the invention will becomeapparent from the accompanying de scription and drawings, which aremerely exemplary.

; In the drawings:

FIG. 1 is an elevational view of the fluid bed furnace according to thepresent invention witha portion of the furnace being shown in sectiontaken along line 1-1 of FIG. 2;

FIG. 2 is a top plan view of the furnace as illustrated in FIG. 1';

FIG. 3 is a sectional view which is in enlarged scale of the sealingelement between the outer shell and the diffusion bottom; and

FIG. 4 is a sectional view taken along the line 43 -4 of FIG. 1, theright half being at a higher level than the left half.

Prececding next to the drawings wherein like reference symbols indicatethe same parts throughout the various views, a specific embodiment ofthe present invention will be described in detail. I

. FIG. 1 illustrates generally at 10 a fluid bed industrial furnaceaccording to the present invention. The furnace 10 comprises main shell11 fabricated of heat resistant metal or alloy and provided with specialheat resistant bottom flanges to absorb thermal expansion. A layer ofinsulation 13, which may comprise a suitable insulation blanket, ispositioned outside shell 11. An outer shell or perforated container 12is used only to contain the insulation.

The shells are positioned upon bottom diffusion member 14 whichcomprises a double layer of porous refractory material arranged withstaggered vertical joints. The diffusion member 14 is supported by aperforated plate 15 which in turn is supported on ventilated piers 16 onplenum bottomplate 17. The entire furnace assembly may be positionedupon supporting legs, comprising a plurality of I beams 18 supportingplate 17. f

A fluid, which may be air or other suitable gas, is introduced throughair inlet 19 from a suitable supply, such as the action of aturbo-blower (not shown).

Within the shell 11 there is located a fluid bed '21,

' which is a mass of non-agglomerative, granular material, through whicha sufficient upward flow of fluid maintains a condition analogous tothat of a fluid. The

bed may comprise silica sand or granular particles of alumina,siliconcarbide or other refractorymaterials.

A cylindrical guard element frame 22 which is somewhat smaller indiameter than the diameter of cylindrical shell 11 is positioned withinthe shell 11 by means On the outer face of the shell 11, adjacent thebottom edge, there is positioned an annular seal 27 which may be securedto the supporting frame of the furnace as shown in FIG. 3. Seal 27 isresilient and may be provided with a plurality of corrugations so as tobear against the outer surface of the diffusion member 14 to prevent thesand or material of the fluid bed from seeping between the edge of shell11 and the diffusion bottom 14 into insulation 13.

The annular ledge 24 also forms a support for a spider which extendsacross the fluid bed from which a heat resistant metal work basket issuspended so as to be immersed into the fluid bed. The work baskets,which are not shown in the drawings, have perforated or open sides andbottom so that the fluidized bed material can circulate through thebasket and around the workpiece contained therein.

The air flowing upwardly through the fluid bed 21 is exhausted throughduct 28 and may be then conducted into a smoke abater as described incopending application Ser. No. 202,223 filed Nov. 26, 1971.

The furnace is closed at its upper end by an insulated cover 29 which isremovable by means of a hoist or opening mechanism 30. The fluid bedfurnace may be be constructed as a pit type or as a bench type suitablefor use in relatively small scale operations.

While the fluid bed furnace of the present invention has been disclosedas being cylindrical in shape, the present invention may also beincorporated in a rectangular furnace, including a furnace having a slotin the cover through which a work basket may be supported from amonorail chain conveyor belt with the work basket being movable throughthe fluid bed.

In operation, air under suitable pressure is introduced through the airinlet orifice into the plenum chamber. As the air in the plenum chamberincreases in pressure, the air will be diffused upwardly through thediffusion member so as to cause the entire fluid bed to fluff slightlyand then settle back to a state resembling a boiling liquid. Upondecreasing the air pressure, the boiling action will decrease graduallyto a completelyquiescence state. If the air pressure is increased, theboiling action will become increasingly violent and gradually becomegeyser-like in appearance. Concurrently with the fluidizing of the bed,the heating elements will be energized so as to heat the bed totemperatures in the range of 200 l,500F. or above, depending upon thematerial of the bed, the heating unit, and the process to be carriedout. The heat is then uniformly diffused throughout the bed and againstthe workpiece or workpieces positioned therein in a work basketsuspended from a spider positioned within the furnace.

The fluid bed furnace of the present invention can be used for manypurposes, especially where a high rate of heat transfer is desirable.One example is heating of aluminum which is a high reflector. Anotheruse would be for removing polymers from dies, screens, piping andsimilar purposes. Still another use is for burning insulation off ofcopper or conductors in electrical machinery so as to recover the scrapmetal. In heat treating of metal, uniformity is attainable. Also, itwould be possible to replace the electrical heating elements withcooling coils (not shown) where it is desired to cool the supportedwithin said shell and immersed in said bed of granular material, saidguard means being spaced inwardly of said shell, and electric heatingelement means in said bed of granular material mounted on the outer faceof said element guard means and spaced inwardly from the inner face ofsaid shell, whereby the entire assembly of the element guard means andheating element means can be removed as a unit from the fluidizable bedof the furnace.

2. In a fluid bed industrial furnace as claimed in claim 1 wherein saidheating element'means comprises a helical coil. v

3. In a fluid bed industrial furnace as claimed in claim 2 and includingceramic insulator means mounting said coil on said guard element means.

4. In a fluidic bed industrial furnace as claimed in 1 claim 1 andincluding means on the inner face of said shell for defining a ledgeupon which said element guard means is supported. 7

5. In a fluid bed industrial furnace as claimed in claim 4 and includingexternal flange means on the upper end of said guard element means andpositionable on said ledge means.

6. In a fluid bed industrial furnace as claimed in claim I wherein saidshell includes a cylinder and said guard element means comprises acylindrical frame of smaller diameter so as to fit within said shell.

7. In a fluid bed industrial furnace as claimed in claim 1 wherein saidshell has a rectangular cross section, the cross section of said guardelement means being similar to that of said shell but being smaller soas to fit therein.

8. In a fluid bed industrial furnaceas claimed in claim 1 wherein saidshell has an insulation means on the outer face thereof, and means atthe bottom of said shell for sealing against the entry of granularmaterial under the bottom edge of said shell into said insulation means.

9. In a fluid bed industrial furnace as claimed in claim 8 whereinsealing means is secured under the bottom edge of said shell againstthetop edge of said porous diffusion member.

10. In a fluid bed industrial furnace as claimed in claim 9 wherein saidsealing means comprises a resilient annular corrugated member bearingagainst the lower portion of said shell to prevent the entry of granularmaterial into said insulating means.

11. In a fluid bed industrial furnace as claimed in claim 9 wherein asealing means bears against the;un-, derside of the porous diffusionmember and the top periphery of the air plenum beneath.

1. In a fluid bed industrial furnace, the combination of a shell havinga porous diffusion bottom member, a fluidizable bed of granular materialwithin said shell on said diffusion member, means for directing fluidupwardly through said bed of granular material to fluidize the granularmaterial, element guard means removably supported within said shell andimmersed in said bed of granular material, said guard means being spacedinwardly of said shell, and electric heating element means in said bedof granular material mounted on the outer face of said element guardmeans and spaced inwardly from the inner face of said shell, whereby theentIre assembly of the element guard means and heating element means canbe removed as a unit from the fluidizable bed of the furnace.
 2. In afluid bed industrial furnace as claimed in claim 1 wherein said heatingelement means comprises a helical coil.
 3. In a fluid bed industrialfurnace as claimed in claim 2 and including ceramic insulator meansmounting said coil on said guard element means.
 4. In a fluidic bedindustrial furnace as claimed in claim 1 and including means on theinner face of said shell for defining a ledge upon which said elementguard means is supported.
 5. In a fluid bed industrial furnace asclaimed in claim 4 and including external flange means on the upper endof said guard element means and positionable on said ledge means.
 6. Ina fluid bed industrial furnace as claimed in claim 1 wherein said shellincludes a cylinder and said guard element means comprises a cylindricalframe of smaller diameter so as to fit within said shell.
 7. In a fluidbed industrial furnace as claimed in claim 1 wherein said shell has arectangular cross section, the cross section of said guard element meansbeing similar to that of said shell but being smaller so as to fittherein.
 8. In a fluid bed industrial furnace as claimed in claim 1wherein said shell has an insulation means on the outer face thereof,and means at the bottom of said shell for sealing against the entry ofgranular material under the bottom edge of said shell into saidinsulation means.
 9. In a fluid bed industrial furnace as claimed inclaim 8 wherein sealing means is secured under the bottom edge of saidshell against the top edge of said porous diffusion member.
 10. In afluid bed industrial furnace as claimed in claim 9 wherein said sealingmeans comprises a resilient annular corrugated member bearing againstthe lower portion of said shell to prevent the entry of granularmaterial into said insulating means.
 11. In a fluid bed industrialfurnace as claimed in claim 9 wherein a sealing means bears against theunderside of the porous diffusion member and the top periphery of theair plenum beneath.